# Baryonic Effects in Cosmic Shear Tomography: PCA Parameterization and the Importance of Extreme Baryonic Models

## Abstract

Baryonic effects are amongst the most severe systematics to the tomographic analysis of weak lensing data which is the principal probe in many future generations of cosmological surveys like LSST, Euclid etc.. Modeling or parameterizing these effects is essential in order to extract valuable constraints on cosmological parameters. In a recent paper, Eifler et al. (2015) suggested a reduction technique for baryonic effects by conducting a principal component analysis (PCA) and removing the largest baryonic eigenmodes from the data. In this article, we conducted the investigation further and addressed two critical aspects. Firstly, we performed the analysis by separating the simulations into training and test sets, computing a minimal set of principle components from the training set and examining the fits on the test set. We found that using only four parameters, corresponding to the four largest eigenmodes of the training set, the test sets can be fitted thoroughly with an RMS $$\sim 0.0011$$. Secondly, we explored the significance of outliers, the most exotic/extreme baryonic scenarios, in this method. We found that excluding the outliers from the training set results in a relatively bad fit and degraded the RMS by nearly a factor of 3. Therefore, for a direct employment of this method to the tomographic analysis of the weak lensing data, the principle components should be derived from a training set that comprises adequately exotic but reasonable models such that the reality is included inside the parameter domain sampled by the training set. The baryonic effects can be parameterized as the coefficients of these principle components and should be marginalized over the cosmological parameter space.

- Authors:

- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Univ. of Chicago, IL (United States). Kavli Inst. for Cosmological Physics
- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Univ. of Chicago, IL (United States). Kavli Inst. for Cosmological Physics and Dept. of Astronomy & Astrophysics

- Publication Date:

- Research Org.:
- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)

- OSTI Identifier:
- 1409075

- Alternate Identifier(s):
- OSTI ID: 1474427

- Report Number(s):
- FERMILAB-PUB-17-223-A; FERMILAB-PUB-18-322-A; arXiv:1707.02332

Journal ID: ISSN 1538-4357; 1609189

- Grant/Contract Number:
- AC02-07CH11359

- Resource Type:
- Journal Article: Accepted Manuscript

- Journal Name:
- The Astrophysical Journal (Online)

- Additional Journal Information:
- Journal Name: The Astrophysical Journal (Online); Journal Volume: 863; Journal Issue: 2; Journal ID: ISSN 1538-4357

- Publisher:
- Institute of Physics (IOP)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTRONOMY AND ASTROPHYSICS; cosmology: theory; gravitational lensing: weak; large-scale structure of universe

### Citation Formats

```
Mohammed, Irshad, and Gnedin, Nickolay Y.
```*Baryonic Effects in Cosmic Shear Tomography: PCA Parameterization and the Importance of Extreme Baryonic Models*. United States: N. p., 2018.
Web. doi:10.3847/1538-4357/aad3b1.

```
Mohammed, Irshad, & Gnedin, Nickolay Y.
```*Baryonic Effects in Cosmic Shear Tomography: PCA Parameterization and the Importance of Extreme Baryonic Models*. United States. doi:10.3847/1538-4357/aad3b1.

```
Mohammed, Irshad, and Gnedin, Nickolay Y. Wed .
"Baryonic Effects in Cosmic Shear Tomography: PCA Parameterization and the Importance of Extreme Baryonic Models". United States.
doi:10.3847/1538-4357/aad3b1.
```

```
@article{osti_1409075,
```

title = {Baryonic Effects in Cosmic Shear Tomography: PCA Parameterization and the Importance of Extreme Baryonic Models},

author = {Mohammed, Irshad and Gnedin, Nickolay Y.},

abstractNote = {Baryonic effects are amongst the most severe systematics to the tomographic analysis of weak lensing data which is the principal probe in many future generations of cosmological surveys like LSST, Euclid etc.. Modeling or parameterizing these effects is essential in order to extract valuable constraints on cosmological parameters. In a recent paper, Eifler et al. (2015) suggested a reduction technique for baryonic effects by conducting a principal component analysis (PCA) and removing the largest baryonic eigenmodes from the data. In this article, we conducted the investigation further and addressed two critical aspects. Firstly, we performed the analysis by separating the simulations into training and test sets, computing a minimal set of principle components from the training set and examining the fits on the test set. We found that using only four parameters, corresponding to the four largest eigenmodes of the training set, the test sets can be fitted thoroughly with an RMS $\sim 0.0011$. Secondly, we explored the significance of outliers, the most exotic/extreme baryonic scenarios, in this method. We found that excluding the outliers from the training set results in a relatively bad fit and degraded the RMS by nearly a factor of 3. Therefore, for a direct employment of this method to the tomographic analysis of the weak lensing data, the principle components should be derived from a training set that comprises adequately exotic but reasonable models such that the reality is included inside the parameter domain sampled by the training set. The baryonic effects can be parameterized as the coefficients of these principle components and should be marginalized over the cosmological parameter space.},

doi = {10.3847/1538-4357/aad3b1},

journal = {The Astrophysical Journal (Online)},

number = 2,

volume = 863,

place = {United States},

year = {Wed Aug 22 00:00:00 EDT 2018},

month = {Wed Aug 22 00:00:00 EDT 2018}

}